//下面是64个基本的编码
 var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 var base64DecodeChars = new Array(
   -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
   52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
   -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
   15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
   -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
   41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);
 
//编码的方法
 function base64encode(str) {
     var out, i, len;
    var c1, c2, c3;
     len = str.length;
    i = 0;
    out = "";
    while(i < len) {
       c1 = str.charCodeAt(i++) & 0xff;
       if(i == len)
       {
             out += base64EncodeChars.charAt(c1 >> 2);
             out += base64EncodeChars.charAt((c1 & 0x3) << 4);
           out += "==";
            break;
          }
      c2 = str.charCodeAt(i++);
       if(i == len)
         {
           out += base64EncodeChars.charAt(c1 >> 2);
            out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
             out += base64EncodeChars.charAt((c2 & 0xF) << 2);
             out += "=";
            break;
          }
       c3 = str.charCodeAt(i++);
       out += base64EncodeChars.charAt(c1 >> 2);
      out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
       out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6));
       out += base64EncodeChars.charAt(c3 & 0x3F);
       }
     return out;
   }
 //解码的方法
 function base64decode(str) {
     var c1, c2, c3, c4;
    var i, len, out;
     len = str.length;
     i = 0;
  out = "";
     while(i < len) {
      do {
          c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
        } while(i < len && c1 == -1);
       if(c1 == -1)
         break;
      do {
          c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
        } while(i < len && c2 == -1);
       if(c2 == -1)
          break;
      out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
      do {
          c3 = str.charCodeAt(i++) & 0xff;
          if(c3 == 61)
            return out;
          c3 = base64DecodeChars[c3];
        } while(i < len && c3 == -1);
       if(c3 == -1)
          break;
       out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
     do {
          c4 = str.charCodeAt(i++) & 0xff;
           if(c4 == 61)
            return out;
          c4 = base64DecodeChars[c4];
         } while(i < len && c4 == -1);
      if(c4 == -1)
          break;
       out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
      }
     return out;
   }
 function utf16to8(str) {
     var out, i, len, c;
     out = "";
    len = str.length;
    for(i = 0; i < len; i++) {
      c = str.charCodeAt(i);
      if ((c >= 0x0001) && (c <= 0x007F)) {
          out += str.charAt(i);
        } else if (c > 0x07FF) {
           out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
            out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F));
           out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
         } else {
            out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F));
             out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
          }
       }
    return out;
   }
 function utf8to16(str) {
   var out, i, len, c;
    var char2, char3;
    out = "";
    len = str.length;
   i = 0;
    while(i < len) {
     c = str.charCodeAt(i++);
    switch(c >> 4)
       { 
      case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
          // 0xxxxxxx
          out += str.charAt(i-1);
          break;
         case 12: case 13:
          // 110x xxxx  10xx xxxx
          char2 = str.charCodeAt(i++);
         out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
         break;
        case 14:
         // 1110 xxxx 10xx xxxx 10xx xxxx
         char2 = str.charCodeAt(i++);
          char3 = str.charCodeAt(i++);
           out += String.fromCharCode(((c & 0x0F) << 12) |
                  ((char2 & 0x3F) << 6) |
                  ((char3 & 0x3F) << 0));
          break;
        }
       }
    return out;
  }
